: Vacuum and dielectric behavior, multipole expansion, and boundary value problems.

"Electricity and Magnetism" by B. Ghosh has several key features that make it a popular textbook:

: Theoretical proofs are broken down without skipping critical intermediate steps.

Electromagnetism is dense with formulas. Dedicate a notebook to writing down core equations (like differential forms of Gauss's law or boundary conditions) from the PDF as you read.